Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014
Deferred tax assets:
Warranty and other reserves	$ 14,913	$ 11,587
Incentive compensation	10,780	18,993
Property, equipment and other assets	2,866	2,750
Federal and state tax carryforwards	292,346	357,146
Inventory adjustments	87,335	95,237
Uncertain tax positions	1,917	1,911
Other	3,814	3,923
Total deferred tax assets	413,971	491,547
Deferred tax liabilities:
Deferred revenues	(30,939)	(43,496)
Total deferred tax liabilities	(30,939)	(43,496)
Net deferred tax assets before valuation allowance	383,032	448,051
Valuation allowance	(57,659)	(445,228)
Net deferred tax assets	$ 325,373	$ 2,823